The present invention relates to a novel process and apparatus for preparing a photopolymerizing lithographic plate, more particularly to an improvement in a process for preparing a photosensitive lithographic plate which realizes preventing a photosensitive layer thereof from lowering its sensitivity. The present invention is also directed to a photopolymerizing lithographic plate produced by this process.
A photopolymerizing lithographic plate is known in the art. Various processes for preparing same have been proposed until now. For example, the invention disclosed in JP-A-10-161317/1998 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined Japanese Patent Kokai Publicationxe2x80x9d) enables to provide a negative imaging lithographic plate capable of direct plate making. A photopolimerizable composition is employed in this lithographic plate. The lithographic plate is highly sensitive to a laser beam especially in the region of visible light and excellent in printing properties such as tone reproducibility, resistance to printing, adhesion of dirt and the like.
However, the following problems have been encountered in the course of investigations toward the present invention. Namely, a more highly sensitizing lithographic plate capable of direct plate making is an everlasting theme. Accordingly, the development of a more highly photosensitive photopolymerizing lithographic plate is required now.
Accordingly it is an object of the present invention to provide an improvement in a process and/or apparatus for preparing a photopolymerizing lithographic plate comprising a coating step and using rubber rollers before and after the coating step. In more detail, the present invention aims at developing a process for preparing a photopolymerizing lithographic plate having a more highly sensitized photosensitive layer.
It is a further object of the present invention to provide an improved photopolymerizing lithographic plate.
The present inventors studied assiduously to improve the process for preparing a photopolymerizing lithographic plate in order to improve the photosensitive layer of the photopolymerizing lithographic plate in terms of sensitivity. Consequently, it was found that the sensitivity is lowered based on an antioxidant (including an aging retardant). This antioxidant contained in a rubber roller is usually used and transferred to the photopolymerizing photosensitive layer to be used. The antioxidant exerts a polymerization inhibition effect upon using the rubber roller in contact with a substrate on a web for handling the substrate for a prolonged period of time or at high temperatures. This can be observed in a process for preparing the lithographic plate including a step of coating continuously the photosensitive layer on the substrate, preferably an aluminum substrate. Then, it was found that lowering the ""sensitivity is prevented and the photosensitive layer having a stable and high sensitivity is obtained by employing a rubber roller or rollers on the surface of which no antioxidant substantially exists. The present invention has been completed on the basis of these findings.
Accordingly, in one aspect of the present invention there is provided a process, for preparing a photopolymerizing lithographic plate comprising a step of coating, in which rubber rollers are used for carrying/conveying a web before and after the coating step. The surface of the rubber rollers to be used at least just before and after the coating step contains substantially no antioxidant and/or aging retardant. Thereby, substantially no antioxidant and/or aging retardant is transferred to a photosensitive layer laminated on a substrate on the web upon using the rubber rollers for a prolonged period of time or at high temperatures.
The rubber rollers exist at least before and after the coating step at a coating site. According to the present invention, it is only required that a surface of at least one rubber roller each positioned just before and after the coating place does not contain the antioxidant and/or aging retardant. It is preferred that the rubber rollers containing the coating surface should satisfy this requirement. In another aspect there is provided an improved product obtainable by the process of the present invention, as well as an apparatus for producing a photopolymerizing lithographic plate in a further aspect.
Other features and aspects of the present invention will become apparent from the entire disclosure, particularly from the appended claims which are incorporated herein by reference thereto.
The present invention also includes following embodiments.
1. The above process in which the rubber roller is a roller whose surface is coated with rubber.
Kinds and shapes of the rubber roller are not limited except it can convey a substrate thereon. For example, such rollers whose surface are coated or covered with rubber as a xe2x80x9croller for conveying a webxe2x80x9d (cf. JP-A-6-144667/1994) are frequently used. These rollers can be reused by changing a wasted coating/cover of rubber with new one. The description concerning the rubber roller found in the JP-A-6-144667/1994 is incorporated herein by reference.
2. The above process in which the substrate is an aluminum substrate.
3. The above process in which the rubber constituting at least the surface of the rubber roller is selected from at least one of ethylene-propylene and urethane rubbers.
As a rubber roller used in the present invention, rubber rollers which are generally in use can be employed. The rubber material used at least on the surface of the roller may be rubber for use in various rollers. Preferably, a rubber roller for carrying/conveying a web can be applied. Ethylene-propylene and urethane rubbers are preferable in view of avoiding decrease in the sensitivity.
4. The above process in which the antioxidant is at least one compound included in phenol, amine and phosphorous series of antioxidants.
According to the present invention, the rubber on the surface of the roller does not substantially contain an antioxidant and/or aging retardant. These agents includes antioxidants and aging retardant which are in general use. Examples of these agents are disclosed in xe2x80x9cHandbook of Chemicals for Rubber and Plastic Formulationsxe2x80x9d (revised second edition, Yoshimichi Mitsumori, xe2x80x9cHandbookxe2x80x9d editorial room, Rubber Digest Co. Ltd.,
5. Aging Retardant, Antioxidant and Antiozonant, p. 76 to 121). Of course, the description of these agents disclosed in this document is incorporated herein by reference.
Concrete examples of these agents include a) naphthylamines such as phenyl-xcex1-naphthylamine and the like, b) diphenylamines such as p-(p-toluenesulfonylamide)-diphenylamine, c) p-phenylenediamines such as N,Nxe2x80x2-diphenyl-p-phenylenediamine, d) other amines such as condensation product of aromatic amine and alophatic ketone and the like, e) mixtures of amines such as mixture of phenyl-xcex1-naphthylamine with diphenyl-p-phenylenediamine and the like, f) quinolines such as polymer of 2,2,4-trimethyl-1,2-dihydroquinoline and the like, g) hydroquinone derivatives such as 2,5-di-(tert-amyl)-hydroquinone, h) mono-phenoles such as 1-oxy-3-methyl-4-isopropylbenzene, i) bis-, tris- and poly-phenols such as 2,2xe2x80x2-methylene-bis-(4-methyl-6-tert-butylphenol), j) thiobisphenols such as 4,4xe2x80x2-thiobis-(6-tert-butyl-3-methylphenol) and the like, k) hindered phenols such as 1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1) phosphites (esters) such as tris(nonylphenyl)phosphite and the like, m) other aging retardants such as dilauryl thiodipropionate and the like, n) coppering retardants and metal-deactivating agents such as 1,2,3-benzothiazole and the like and o) waxes such as specialty wax and the like.
It is preferable from an aspect of the effect on avoiding the decrease in the sensitivity that the rubber does not contain antioxidants (also aging retardant), especially, phenol, amine and phosphorous series of compounds among them.
Concerning the usage of antioxidant and/or aging retardant, no use is recommended because it is the best way. Usual usage of these agents, which is effective for improving rubber characteristics such as resistance to oxidation, aging property and the like, ranges, for example, from 0.1 to 10% by weight, preferably, from 0.5 to 5% by weight. However, these degree of the usage causes adverse effects. Accordingly, it is involved in the process of the present invention to use the agent in a slight amount to such an extent that these effects do not appear, or it is substantially not transferred to the photosensitive layer laminated on the substrate to be carried/conveyed.
5. A photopolymerizing lithographic plate produced by the above process.